PIC Microcontoller Radix Math Method

10bit to BCD unpacked 4 digit in 38 inst ~88 cycles by E. A. Grens

10 bit Binary to BCD Conversion

Posted on the Chat Zone by Ed Grens on September 22, 2004 at 03 08 38

On 18 September Peter Hemsley posted a 12b binary to BCD conversion subroutine in a response to a post by me. His algorithm is excellent for 12b conversion, but not efficient for the 10b often encountered with A/D inputs. Over the 10b data range, 0x000 to 0x3FF, this routine requires on the average of 131 processor cycles. Actually this is more than it requires on the average over the entire 12b range (118 cycles).

A simple divide by power of ten algorithm, listed below, requires on the average 88 cycles over the 10b range. This is possible because, for 10b, one can use single byte subtractions for divides. At 12b (probably) and certainly at 16b this approach cannot compete with the procedure Peter has presented. But, if 10b is what you need, it can be advantageous.

Ed +

Code:

•   ;======= Bin2Dec10G.asm ============= Sep 04 =========
    ;       Test of 10b binary to 4 digit conversion as 
    ;       based on division by powers of 10. 
    ;
    ;       E. A., Grens
    ;
    ;       For most PICs - here for 16F628 with 4 MHz
    ;       internal oscillator.
    ;
    ;       Average processor cycles for execution of
    ;       subroutine over the input range 0x000 to 0x3FF
    ;       is 88.  No variables required except the
    ;       input blh, blo and the out BCD digits.
    ;       Subroutine length 38.
    ;======================================================
  
          list p=16f628
          radix   dec
          #include 
          __config 0x3D30
  
    
    ;-------Set Up RAM Variables---------------------------
    blo   equ     0x20            ;lsbyte of 10b binary
    bhi   equ     0x21            ;msb
    d4    equ     0x23            ;msdigit
    d3    equ     0x24
    d2    equ     0x25
    d1    equ     0x26            ;lsd
    ;-------Program Code--------------------------------
                                           
          org     0x00            ;Effective Reset Vector
    ;
          nop
          goto    Start           ;Jump by interrupt
    ;
    Start
          movlw   0x07
          movwf   CMCON           ;Digital I/O
          movlw   0x03            ;Test input
          movwf   bhi
          movlw   0xFF
          movwf   blo
          movlw   0x04
          call    Bin2decg
    Hold
          goto    Hold            ;Finished
  
    Bin2decg                      ;10b binaey to BCD
          clrf    d1
          clrf    d2
          clrf    d3
          clrf    d4
          clrc
          rrf     bhi,f           ;N = 4*Q + R
          rrf     blo,f           ;blo = Q
          rrf     d1,f            ;d1 = R as temp, R25 
          goto    B2d2            ;repeat
    B2d3
          addwf   blo,f           ;get remainder
                                    ;    after /100, C = 0
          rlf     d1,f            ;*4 and add R back in
          rlf     blo,f
          rlf     d1,f
          rlf     blo,f           ;4*blo + R = N - 
                                    ;    1000*d4 - 100*d3
                  movlw   10
    B2d4
          subwf   blo,f           ;blo = N - 1000*d4 -
                                    ;     100*d3 - 10*d2
          skpc
          goto    B2d5            ;blo10
          goto    B2d4
    B2d5
          addwf   blo,f           ;put last 10 back, C=0
          movf    blo,w            
          movwf   d1
          return
     
          end
  
        
  **********************
  
  12-bit code
  
  Posted by Peter Hemsley on September 18, 2004 at 17 40 56 
  Message   ; Bonus 12-Bit version
  
    ; Leaner and Meaner, 36 instructions
    ; Ideal for displaying A/D values
    Bin2DecFast
          movf    NUMHI,w
          iorlw   0xF0            ;w=H2-16
          movwf   D1              ;D1=H2-16
          addwf   D1,f            ;D1=H2*2-32
          addwf   D1,f            ;D1=H2*3-48
          movwf   D2              ;D2=H2-16
          addlw   -D'5'           ;w=H2-21
          addwf   D2,f            ;D2=H2*2-37 Done!
          addlw   D'41'           ;w=H2+20
          movwf   D0              ;D0=H2+20
  
          swapf   NUMLO,w
          iorlw   0xF0            ;w=H1-16
          addwf   D1,f            ;D1=H2*3+H1-64
          addwf   D0,f            ;D0=H2+H1+4, C=1
          rlf     D0,f            ;D0=(H2+H1)*2+9, C=0
          comf    D0,f            ;D0=-(H2+H1)*2-10
          rlf     D0,f            ;D0=-(H2+H1)*4-20
  
          movf    NUMLO,w
          andlw   0x0F            ;w=H0
          addwf   D0,f            ;D0=H0-(H2+H1)*4-20 Done!
          rlf     D1,f            ;C=0, D1=H2*6+H1*2-128 Done! 
  
          movlw   D'5'
          movwf   D3
  
          movlw   D'10'
    mod0
          addwf   D0,f            ;D(X)=D(X)mod10
          decf    D1,f            ;D(X+1)=D(X+1)+D(X)div10
          skpc
          goto    mod0
    mod1
          addwf   D1,f
          decf    D2,f
          skpc
          goto    mod1
    mod2
          addwf   D2,f
          decf    D3,f
          skpc
          goto    mod2
  
          return
  
  

  +

See also:

• ftp://ftp.epemag.wimborne.co.uk/pub/PICS/PICtricks/10%20and%2012%20bit%20Binary%20to%20BCD%20Conversions.txt +

Comments:

• ve2ulu@spam@ at KILLspamcgocable.ca

  The 12 bit conversion routine, to use on PIC18, change all DECF for DECFSZ with NOP after.
  DECF change carry on PIC18, not DECFSZ!
  And also for all, SKPC, GOTO MODx change for BNC MODx

  +
• Thanks, SECOND code (for 12 bit) is working good! But 1st is not full and doesn't working. The string "goto B2d2" pointing to nothing and if this label points earlier than "B2d3" code is looped forever 'cos there's no any branch instructions.+
• teemu.ramo@spam@ at KILLspamgmail.com " txt-file line 78 there's goto B2d2 which is not defined in this code. At least that seems to be missing" James Newton of MassMind replies: Ah... yes... something seems to be missing. If anyone knows the author, please ask him if he is willing to provide a correction.+

  +

• The 10 bit conversion routine seem to be incomplete. James Newton replies: In what way?+

  +

Michael Lee Van Dyke Says:

On the 10 bit code, the 9th instruction after the Bin2decg label is is "goto B2d2". There is no B2d2 label in the code, it will not work as it is written here.

Questions:

• The asm code for 10bit2BCD has a line "goto B2d2" but there is no corresponding label. The comment for the same line says "repeat" but there is no loop counter, so I can't patch the code. What am I missing? James Newton of MassMind replies: Not sure... Only the author would know.+

  +

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